1. Field of the Invention
The present invention relates to a solid-state imaging apparatus and a method of driving the same.
2. Description of the Related Art
In recent years, solid-state imaging apparatuses, such as CMOS image sensors, have been achieving high performance and high functionality. One of these achievements is advancement in multi-pixel configuration of imaging devices for providing high resolution images. Accordingly, the number of circuits for reading pixel signals is increased, which in turn increases consumption current and also increases drop in voltage of a power source line. Thus, operating points of read out circuits connected to a common power source line are different depending on the positions, which causes horizontal shading.
To address this problem, Japanese Patent Application Laid-Open No. 2001-197378 takes measures to hold the gate voltage of a current source transistor, which supplies current to read out circuits (column circuits) arranged for respective columns, in a capacitor connected between a reference potential and the gate of the current source transistor during the column circuit being not in operation. In a period when the column circuit does not operate, that is, without drop in voltage of a power source line, the gate voltage of the current source transistor is held in the capacitor connected to the reference potential. Accordingly, even if the power source (reference) voltage drops after the column circuit operates, the gate voltage, i.e. voltage Vgs, of the current source transistor with respect to the reference potential becomes constant and thus the current values of the column circuits become the same. The problem of horizontal shading is therefore alleviated and solved.